Battery packs provide power for various technologies ranging from portable electronics to renewable power systems and environmentally friendly vehicles. For example, hybrid electric vehicles (HEV) use a battery pack and an electric motor in conjunction with a combustion engine to increase fuel efficiency. Battery packs are formed of a plurality of battery modules, where each battery module includes several electrochemical cells. The cells are arranged in two or three dimensional arrays and are electrically connected in series or in parallel. Likewise, the battery modules within a battery pack are electrically connected in series or in parallel.
Different cell types have emerged in order to deal with the space requirements of a very wide variety of installation situations, and the most common types used in automobiles are cylindrical cells, prismatic cells, and pouch cells. Regardless of cell type, each cell may include a cell housing and an electrode assembly disposed in the cell housing. The electrode assembly includes a series of stacked or rolled positive electrode plates that alternate with negative electrode plates and are separated by an intermediate separator plates. Each cell may also include a first current collector that is electrically connected to the positive electrode plates and joins the positive electrode plates to a positive cell terminal disposed outside the cell housing, and a second current collector that is electrically connected to the negative electrode plates and joins the negative electrode plates to a negative cell terminal disposed outside the cell housing.
In a pouch cell, the first and second current collectors typically each include a lead tab that passes out of the pouch between two stacked layers of pouch fabric and along a weld line that joins the layers of pouch fabric together and forms a sealed joint. The lead tab is used to pass current from inside the pouch cell housing to the outside where it can be electrically connected to an external structure such as a terminal. A sealing tape having specialized material properties is applied to each side of the lead tab at the sealed joint where the lead tab passes between the layers and out of the pouch. The sealing tape is hot melted to the inside layer of the metal foil laminate material used to form the pouch cell housing.
It is advantageous to be able to quickly charge and discharge the electrochemical cell. The rate of charge or discharge is due at least in part to the cross sectional area of the lead tab, where an increased lead tab thickness results in reduced electrical resistance and increased current carrying capacity. However, increased lead tab thickness sometimes results in gaps being formed between the sealing tape and the lead tab at the ends of the lead tab. Thus, it is desirable to provide a lead tab that has sufficient thickness to meet current carrying capacity requirements while forming a reliable seal with the pouch cell opening via the sealing tape.